The production of carbon and graphite bodies having controlled properties has been the subject of much research. In recent years, bodies produced from pitch, and in particular, mesophase pitch, have shown remarkable properties in flexural resistivity, density and other areas.
U.S. Pat. No. 3,943,213 describes the mixing of from 1 to 50 weight percent chopped carbon fibers in a hot fluid mesophase system, the forming or casting of a shaped article from the mixture, and the subsequent graphitization of the shaped article. The composite product is described as having enhanced structural properties, although no directional properties are disclosed.
Other patents also disclose the production of shaped carbonaceous bodies made from pitch-based precursors. U.S. Pat. No. 3,546,076 describes a method of producing metallurgical coke briquettes comprising heating pitch-based raw coke particles having a volatile content of 10 to 20 weight percent to a temperature between 300 and 525.degree. C., preferably between 325 and 470.degree. C., applying sufficient pressure to cause the hot particles to adhere to each other. and form the briquettes, and then carbonizing the briquettes. Raw coke particles having a volatile content as low as 8 weight percent may be used if mixed with higher volatile content coal. The coke briquettes are not disclosed as having anistropic properties.
U.S. Pat. No. 4,071,604 describes the production of carbon bodies from carbonaceous pitch that has been advanced to a plastic amorphous precursor to coke having 3 to 11 weight percent volatile content. The carbon bodies made from the coke precursor are isotropic in nature, having been comminuted in the precursor stage, pressure shaped, and carbonized.
The following patents relate to the production of anisotropic carbon bodies from pitch, specifically mesophase pitch:
U.S. Pat. No. 3,787,541 describes a process for producing graphite bodies by extruding mesophase pitch having at least 22% volatile content and subsequently carbonizing and graphitizing the extruded pitch. The patent describes the spinning of thin fibers under 0.3 mm in thickness and the extrusion of larger bodies of 2.5 inches (63.5 mm) thickness. The coefficient of thermal expansion (CTE) of molded bodies is given as from 1.5 to 8.times.10.sup.-6 .degree.C..sup.-1 in the molding direction and from 0.5 to 8.times.10.sup.-6 .degree.C..sup.-1 in the transverse direction.
Improvements in graphitizable carbon fibers are disclosed in U.S. Pat. No. 4,005,183. The patent discloses that anisotropic carbon and graphite fibers may be produced by spinning and heating fibers made from greater than 85 weight percent mesophase. However, the high viscosity of 85 weight percent mesophase makes such spinning very difficult. That patent further describes the production of highly anisotropic carbon and graphite fibers from pitch having less than 85 weight percent mesophase by spinning the pitch into fibers, thermosetting the fibers by heating in oxygen, and then carbonizing and graphitizing the givers. The oxidative thermosetting step makes possible the preservation of the crystal orientation of fibers produced from pitch containing less than 85 weight percent mesophase.
British Pat. No. 1,526,809 describes the forming of an extruded graphite article by inclusion of oriented anisotropic carbon shapes such as rods, bars, filaments or sheets produced from pitch having from 40 to 90 weight percent mesophase. The as-formed mesophase pitch shapes are oxidatively thermoset before carbonizing as in the previously discussed patent. Graphite articles produced by this method were found to have exceptionally low coefficients of thermal expansion (CTE) in the longitudinal direction.
In the prior art practice exemplified by U.S. Pat. No. 4,005,183 and British Pat. No. 1,526,809, the remaining volatile components of the mesophase pitch are largely expelled after the pitch fibers have been rendered infusible by oxidative thermosetting. Without this additional step of oxidative thermosetting, the as-formed pitch fibers cannot be converted to carbon and graphite without melting. The oxidative thermosetting that is necessary in this practice may also inhibit the carbon from developing fully the three dimensional order of polycrystalline graphite. In addition, the core regions of thicker shapes cannot retain their orientation during carbonization because oxygen generally cannot diffuse beyond a relatively thin surface layer.
Based on the state of the art, there is a need for highly anisotropic, controlled property carbon and graphite bodies in shapes other then thin fibers and a method of producing same in which oxidative thermosetting is not required to prevent melting and resultant loss of orientation during carbonization and graphitization.